Our studies on oxygen toxicity in the red cell rely on the use of drugs as biochemical probes. In our initial approach we studied the interaction of cell components with drugs. In this application we concentrate our efforts on cellular studies to gain an understanding of the influence of drugs on cellular metabolism and changes in the intracellular environment. Our protocols approach questions concerning the interrelationships that exist in the red cell among oxygen metabolism, hemoglobin function and glycolysis. We also present experiments that focus on the role of ascorbate and metal catalysis in cellular toxicity. We measure flux of glucose metabolism, intracellular nucleotide concentration, glutathione turnover, intracellular pH, oxygen consumption, hydrogen peroxide concentration and activities of enzymes that catalyze the removal of the reduced products of oxygen metabolism, such as superoxide and hydrogen peroxide. There studies should yield insight into the biochemical mechanisms evolved for handling oxygen and should enhance our knowledge of the biochemical function of the red cell.